Two Eclipses 2023-2024

April 8 2024 Monday Total Eclipse

Warning for April 8 2024 total eclipse:  Eye danger for children who can't follow directions during excitement!  Outside the 3 minutes of totality, you will burn your retinas if you stare at the partially eclipsed sun.  Adult supervision is needed, second by second, for young students.  If you are squinting at a bright Sun, it is not the time of "totality," and the sunlight is too bright for your eyes;  put on your commercial eclipse viewer or look at the Sun image from a pinhole camera, or look for the light arcs under a tree.  Read about Bailey's Beads, they are very brief and safe to look at.

The east part of San Antonio is not a place to see the total eclipse on April 8, 2024.  Southwest San Antonio will see totality for 2.5 minutes or so and will still have horizon light and city night light from street lights, not pitch black.  Castroville is not the right direction to travel, there will be only 2.5 minutes of totality.  Bandera is the better choice, for 4 minutes 3 seconds.  Kerrville is optimum.  Bandera and Kerrville, in spots away from parking-lot lights, will have fairly dark skies and the best view of the solar corona.

During totality, waste no time taking off your eclipse glasses.  The Sun's corona will be visible for only minutes.  Glace all around the horizon for the edge of sunlight, for stars, and for planets.  Listen for bird and insect sounds.  Spend no time looking for the Moon!  The Moon is an invisible full Moon, blocking the Sun.  Look at the ground (especially at a white bedsheet stretched out flat) just before and just after totality for the rare "shadow bands" running along at five miles per hour.  (Wikipedia shadow bands, and listen to the movie for typical crowd excitement)

There is a reason to stare at the fully eclipsed sun during the three minutes of totality:  this day is the only time most people will ever see the Sun's corona live, amid the excitement of dusk falling at double speed and with a different quality than normal dusk.  There is a sense of a strange, perhaps alarming, dark shadow coming from the southwest (for the Ap 8 2024 eclipse, not from the east like normal dusk!) and coming down from above (normal dusk comes from the horizon), then dark hits and a waning light briefly is seen, departing to the northeast.  And stars are visible like at midnight, especially if you are away from parking-lot lights and street lights, as soon as your eyes adjust to sudden pitch black.  If the viewer is part of a group, excitement is enhanced by the exclamations you hear from the group.

The strangeness is enhanced by the suddenness.  We are all accustomed to dusk or dawn going on for about 90 minutes.  But a total eclipse brings on a dusk that seems to be only four minutes long.  This brevity is because the pupils of our eyes compensate for most of the 80-minute reduction of sunlight as the Moon gradually eclipses the Sun, then we realize in the last four minutes or even 15 seconds before totality that something strange is happening.  The strangeness is why nontechnical cultures fear eclipses, especially total solar eclipses;  total eclipses are so rare, there is usually no one who remembers the previous one.

The Sun's corona is a non-uniform light around the Sun that appears static during the eclipse.  With a coronagraph at a major observatory, astronomers view the corona for hours at a time and do see changes, which dovetails with the high speed of ions in the corona, which are going at hundreds of thousands of miles per hour because their temperatures are a million degrees.

If your viewing spot is near a road, beware drivers who are unaware of the eclipse.  In their surprise, drivers will fail to turn on headlights.

Remember that a total eclipse happens along a path that is only 125 miles wide for this eclipse.  The average person will see at most one total solar eclipse in a lifetime.  Near cities, due to traffic congestion, some who intend to travel to the path of totality are tied up in congestion, including congestion along rural roads.  In the final minutes before totality, beware RV drivers suddenly pulling over in desperation and not totally clearing the traffic lane.

In the day following your total eclipse, sit down and write a description of your experience.  Pass this down to your grandchildren.  Write about the exclamations you heard from people around you.  If you are a student in a school but are allowed to look at the corona, write about the different fears of teachers---they don't want to be sued for causing you blindness, and the more the fearful tales teachers hear, the less likely they are to let students be outside.  But once "night" falls, it is safe to stare at the corona, even with binoculars.  Just don't expect the corona to be big--it is just a little bigger than the full Moon.

https://nso.edu/for-public/eclipse-map-2024

This eclipse map is special because you can zoom to your location and click, and a window pops up giving duration and other info.  

The edge of totality sweeps from the Macdona community to the intersection of 151 at 90, northeastward through Alamo Quarry Market, and beyond.  Because the sine of an angle rapidly increases from zero degrees, the duration of totality rapidly increases for every mile inside the edge of totality.  At Leon Valley, six miles from the edge, totality is 1 minute 55 seconds.  At Straus Middle and Kallison Elementary, 13.3 miles from the edge, totality is 2 minutes 41 seconds.   This is where sunlight from areas eastward (areas not totally eclipsed) will be less visible on the horizon.  At Bandera, 38 miles from the edge, totality is 4 minutes 5 seconds.  Bandera has the advantage of being near the dark-sky area of the Hill Country (only if you are away from parking-lot lights), so that the corona and stars will be easier to see.

Familiar constellations during the total eclipse are few.  The Big Dipper is too low on the north horizon.  The little, stretched W of Cassiopeia is high overhead, as is the big rectangle of Pegasus.  The bright six stars of the Cygnus cross are overhead.  It is not possible to familiarize oneself with the eclipse constellations by looking at nighttime constellations a week ahead of the eclipse, because the eclipse constellations are daytime constellations, twelve hours removed from October nighttime constellations!

// ARDUINO CODE  JE 10-13-2022 using CdS and thermistor hardware set of which we have 4 qty

// file name   analogInputsCdSforAnnularEclipse_v1.ino    for STEM Club

// 7200 seconds in 2 hrs, if the graph is 500 samples long then each sample is 14.4seconds

unsigned long sum_CdS;

int avg_qty = 48;   // this works with delay(300) to make 14.4/.3=48 samples averaged 

int LED_count = 0; byte LEDpin = 4; byte LEDgrnpin = 5;  //LEDpin yellow

void setup() {

  Serial.begin(9600);

  pinMode(LEDpin,OUTPUT);  pinMode(LEDgrnpin,OUTPUT);

}

void loop() {

  sum_CdS = 0;  LED_count = 0;

  for(int ct =0;ct<avg_qty;ct++) {

    sum_CdS += analogRead(1);

    delay(300);  LED_count += 1;

    if (LED_count %2 == 0 ) {  digitalWrite(LEDpin,true); }

    else digitalWrite(LEDpin,false);

    if (LED_count>(avg_qty-5)){ digitalWrite(LEDgrnpin,true); }

    else digitalWrite(LEDgrnpin,false);  

  }

  Serial.println( sum_CdS / avg_qty );  //specially good for Serial Plotter

}

Shadow Bands

In preparation for April 8 total eclipse, John E thoughts about "shadow bands," the mysterious, thin, moving bands of light, sort of zebra stripes, that are sometimes seen in 15 seconds before a total eclipse, and after.   I want to make an electronic device to record shadow bands, with a frequency range up to 50Hz or 300Hz.  It may be that the shadow bands are always there, not rare, and that they go at higher frequencies that the eye can't follow.  The simplest sensor would be one phototransistor with a nonlinear load (diodes and resistors, giving voltage output over a 1000:1 light range) feeding into a VFO so that even DC light produces an audio signal.  If shadow bands appear, they would modulate the audio.  This could be recorded by a smart phone, which could be recording video of shadow bands on a white sheet.  

     The single phototransistor could be elaborated.  Use two or three phototransistors with varying load resistors, buffer each with an op-amp follower, and sum the signals with an adder.  Then go into the VFO.  Another elaboration would be a windowing comparator that delivers only one phototransistor signal at a time to the VFO, the one that is closest to mid-range.  (Could be done with an Arduino.)  LEDs would signal which phototransistor is active.  At this rate, five phototransistors could be used, because sunlight in the minute before totality might vary over a 100,000:1 range.  Or more?  

     Such a sensor could be tested by shining an LED at the sensor, with the LED current modulated by a sine wave.

     I had speculated earlier about a square array of phototransistors, all of them being recorded in parallel, which could be used to determine the direction of the shadow bands, by doing correlation (with time shift) between all pairs of phototransistors.  This would be a much bigger setup.